1. Field of the Invention
The present invention generally relates to instruments for use in oil and gas drilling operations and more particularly to apparatus for transporting such instruments within a well.
2. Background of the Invention and Description of the Prior Art
Transporting oil and gas instruments and tools within a well bore is typically accomplished by gravity for vertical wells and with water pumped under high pressure for wells that have laterals or horizontal paths. In the latter case, after the tool or other instrumentation is lowered into the well bore and suspended on the wireline, water is pumped in high volumes under high pressure into the well to force the tool package through the well casing. A typical tool has a diameter that presents some obstruction in the casing to the flow of water to enable the water pressure to push against the tool, forcing it along the interior of the casing. Nevertheless, because the tool is not a complete obstruction to the flow of water, a substantial portion of the water flows past the tool below or beyond the position of the tool in the well.
The disadvantages of this “lost” or wasted water, and the additional pump pressure required to compensate for the losses due to leakage past the tool, include the use of more water lost to other beneficial uses, the need for more powerful pumps and the excess energy required to develop sufficient pump pressure to overcome the losses due to the lack of full obstructive effect of the tool, and the extra time required to complete the transport of the tool to the desired position in the well. Other disadvantages include the inability to transport a tool in badly deviated wells, contamination of more water than necessary if the amount of water required could be reduced, reduced washing effects on composite plugs that are located below the tool being transported, and of course the monetary losses that accompany these inefficiencies. This problem, if solved, would substantially improve the efficiency of operations in horizontal wells, particularly in the placement and recovery of tools and the like.
The prior art includes devices that, when sized for use in a well casing of a known diameter can be used to alternately provide a blocking effect or a pass-through feature responsive to the hydrostatic pressure in the well bore. As a blocking device attached to an instrument string, the instrument string can be fixed in a desired stationary position in the well bore. As a pass-through feature, fluid is allowed to flow freely through the device and the well casing. Such a device is disclosed in U.S. Pat. No. 4,399,840 issued to Baugh et al., which “has a ball [adjustable] between an open position to allow flow through the drill string for testing and a closed position to block flow. Operating means convert the ball between an open and closed position in response to pressures in the well annulus.” However, to adapt such a device to the objective of moving or conveying an instrument through a well casing, the ball or other blocking device would need to be carefully sized for use in each specific casing size, so as to obstruct the flow of most of the fluid past the device but not such a close fit within the casing as to not move freely through the casing. Moreover, due to the variety of casing sizes and the likelihood of variation in the inside diameter of well casings, such a device would be impractical because of the associated costs and compromises to provide a device that would work reliably regardless of the casing inside diameter. For example, a different size blocking device would be required for each casing diameter, and the associated housing and support structure for accommodating each size, including the mechanism for changing its orientation with respect to the direction of flow, would be expensive in both costs of manufacture and operation.
Another prior art device is a well packer, a device that is configured for blocking and sealing a well casing at some desired location fixed within the well bore. Some are formed by mechanical structures such as sliding wedges that have surfaces to conform to the circular well casing that can be operated to expand after placement into a stationary position to occupy the entire cross section of the well casing. These tend to be complex and typically require sealing to be effective in “packing” the well bore, i.e., acting as a plug in the well casing. Others may be constructed as inflatable devices. While these may be adaptable to differing well casing diameters, and may even be able to provide the sealing action required in a packer, they require a mechanism to inflate them, which may be an added complexity in their use. Further, packers are intended to be installed at a desired position and left in place. A well packer is used as a stationary device to plug the well at a desired location. It is not intended to move to fulfill its function. This is in contrast to the need to provide a device that must move readily to transport or convey a tool through a well bore, including a horizontal well, to a specific location using water pressure, and thereafter removing the device because it is no longer needed for moving the tool.
What is needed is a practical way to reduce the amount of water and water pressure required to transport a tool through the casing, while speeding the process to accomplish the objective in less time. A practical solution must be inexpensive to manufacture, easy to use, reliable, reusable, and able to withstand the severe operating conditions found in a well bore, particularly one involving substantial lateral passages and passages that are badly deviated. A deviated well is one in which the well bore deviates from the vertical direction, as in horizontal drilling or changing the course of the well bore to reach an objective not in a vertical line with the well bore at the surface.